Barrett's esophagus (BE) is the replacement of the normal squamous esophageal epithelium with an intestinalized columnar epithelium. It occurs in response to chronic acid and bile reflux and is an important risk factor for the development of esophageal adenocarcinoma (EAC). BE is thought to be an adaptive response to chronic tissue injury and the release of pro-inflammatory prostaglandins and cytokines. However, the mechanisms underpinning BE pathogenesis remain poorly understood in part due to the paucity of experimental animal models. The development of innovative, genetically based and physiologically relevant mouse models for BE is an important long-term objective of my lab. Cox-1 and Cox-2 are the rate-limiting enzymes in prostaglandin biosynthesis. Cox-2 expression is induced in the esophagus by acid reflux, and the inhibition of Cox-2 reduces the progression to BE and cancer in a rat bile reflux model. Cox-2 is also known to increase intracellular oxidative stress and damage DNA. Nevertheless, a role for Cox-2 in the pathogenesis of BE and EAC has not been tested. We have utilized a novel 3D in vitro cell culture system to model BE pathogenesis. When we express Cox-2 in normal human esophageal keratinocytes we observe the development of intestinal mucin-filled cysts. This suggests that Cox-2 expression is sufficient to induce an altered cell lineage from keratinocytes, one that has mucin-secretory features consistent with BE cells. We therefore hypothesize that Cox-2 expression in the murine esophagus results in a chronic esophagitis that models GERD esophagitis by provoking oxidative stress, DNA damage, and the development of metaplasia and dysplasia. The rationale for the proposed research is that while a role for Cox-2 in the pathogenesis of Barrett's esophagus is suggested by clinical observational data, this has not been proven in animal models. Once it is established, greater consideration can be given to pharmacological approaches to prevent the onset of BE and limit progression to cancer. Guided by strong preliminary data, this hypothesis will be tested by the following inter-related Specific Aims: 1) Does chronic Cox-2 activity in the esophagus of K14-Cox2 mice result in inflammation, oxidative stress, DNA damage, and the adoption of an altered differentiation program? 2) Can a diminished antioxidant response or defective DNA repair synergize with esophageal Cox-2 expression to accelerate the onset of DNA damage, metaplasia, and dysplasia? Summary BE is an increasingly common precancerous condition and an emerging U.S. health problem. Our studies are significant because they mechanistically explore the contributions of Cox2 to BE pathogenesis, and we anticipate our approaches will yield improved mouse models for BE. Additionally, as a Midcareer Investigator Award, this study will provide an outstanding focus for the PI to: 1) advance his skills in mouse pathobiology research and comprehensive phenotyping; 2) serve as a basis for mentoring of junior investigators in these areas; and 3) Conduct state-of-the-art biomedical research in mouse pathobiology.